When, after an injury or harm allegedly caused by an event, measures are taken that, if taken previously, would have made the injury or harm less likely to occur, evidence of the subsequent measures is not admissible to prove negligence, culpable conduct, a defect in a product, a defect in a product's design, or a need for a warning or instruction. This rule does not require the exclusion of evidence of subsequent measures when offered for another purpose, such as proving ownership, control, or feasibility of precautionary measures, if controverted, or impeachment.

Usually, this rule applies when an instrumentality causes an injury and the defendant subsequently makes the instrumentality safer. For instance, if a patron falls on the front steps at a restaurant, evidence that the restaurant subsequent changed the lighting or added a handrail to the steps would be inadmissible under the rule. And if a child chokes on a toy, evidence that the manufacturer subsequently made the toy bigger would be inadmissible under the rule. As the recent opinion of the United States District Court for the Southern District of New York in Hamilton v. City of New York, 2009 WL 2973007 (S.D.N.Y. 2009), makes clear, however, the rule also applies to changes to allegedly discriminatory hiring practices.

In Hamilton, the plaintiffs were four current and former employees of the NYPD Crime Laboratory who claimed they were discriminated against based on their race and national origin and, as to two of the four, gender. These plaintiffs claimed they were denied promotions and demoted while promotions were given to less qualified Caucasian males who were born in the United States. Specifically, these plaintiffs alleged, inter alia, that when two new Criminalist IV positions were created, employees were not notified that they could apply for these positions, nor were interviews conducted. Instead, their supervisor merely offered these positions to Caucasian males and did not consider seniority in choosing candidates for promotion.

In support of their claims, the plaintiffs sought to present evidence that, "after the 2005 promotions, defendants changed their practices, and began posting new positions so that any interested applicant could apply, which plaintiffs argue is evidence that defendants knew their previous practices were discriminatory and unfair." The court, however, found that this evidence was inadmissible because it constituted a subsequent remedial measure under Federal Rule of Evidence 407. As support for this conclusion, the court relied upon two prior opinions that had similarly found that changes in employment practices after alleged discrimination are inadmissible under the rule because they constitute subsequent remedial measures.